Lattice Location and Photoluminescence of Er in GaAs and Al_0.5Ga_0.5As

Abstract

Epitaxial Er-doped GaAs and Al0.5Ga0.5As films, 1.6 μm thick, grown by MBE on (100) GaAs substrates at 560°C, with Er concentrations in the range 9 × 1017 to 2 × 1020 cm−3 were studied with RBS/channeling and photoluminescence techniques. Angular scans in the <110> and <111> axial and (111) planar directions indicate that the Er atoms in GaAs are located on interstitial sites. In Al0.5Ga0.5As doped with 5 × 1019 Er cm−3, 70% of the Er atoms are on positions slightly displaced from the interstitial site, the rest presumably substitutional. In Al0.5Ga0.5As doped with 9 × 19 Er cm−3, more than 88% of the Er atoms are on substitutional sites.Photoluminescence around 1.54 μm is observed at room-temperature in Er-doped Al0.5Ga0.5As. Both the low and highly Er-doped samples show similar luminescence intensities; the luminescence lifetimes are on the order of 1 ms. The Er-doped GaAs does not show any measurable signal at room-temperature. Correlation of the luminescence data to the Er lattice location suggests that only substitutional Er in AlGaAs is in the luminescent trivalent state.

Lattice Location of Rare Earth Ions in Semiconductors and Their Optical Activity

“…Observations on Er-implanted GaAs have been recently confirmed by lattice location measurements performed on molecular beam epitaxy (MBE) grown GaAs:Er epilayers [18]. Alves et al [18] have shown that directly after the growth at 5500C the Er atoms were located at the tetrahedral interstitial positions.…”

“…Intense intra-atomic luminescence of Er3+ could also be observed in as-grown samples. The authors have found that in MBE grown AlGaAs:Er a significant substitutional fraction of Er atoms exists, but no Er-related luminescence could be detected in this material [18].…”

“…Alves et al [18] have shown that directly after the growth at 5500C the Er atoms were located at the tetrahedral interstitial positions. Intense intra-atomic luminescence of Er3+ could also be observed in as-grown samples.…”

“…In the light of channeling experiments performed on Er-implanted [17], MBE grown GaAs:Er, doping at the impurity level [18], and in ultra thin ErAs layers in GaAs [19], an interstitial location of optically active Er seems to be well established. However, the reasons of such unexpected correlation remains unclear.…”

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“…On the experimental side, a number of RBS lattice location studies revealed the following trends. In general, samples doped with Er during metalorganic chemical vapour deposition (MOCVD) [40][41][42] or molecular beam epitaxy (MBE) [43][44][45] showed the majority of Er in near-tetrahedral interstitial locations with respect to the GaAs lattice irrespective of Er concentration. In implanted samples, Er was found to prefer substitutional sites at concentrations around 10 19 cm -3 but tetrahedral interstitial around 10 20 cm -3 [46,47].…”